A baby was the youngest injured in a serious head-on crash overnight in Auckland.

The six-month-old was extricated from one of the cars about 9pm following the two-car crash on the Kaipara Coast Highway in Rodney, at Glorit.

There were believed to be half a dozen passengers in the two cars.

A woman in her 40s had serious injuries and two others had moderate injuries. The woman's baby had minor injuries.

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Auckland Rescue Helicopter chief crewman Mark Cannell carrying the injured child. Photo / Supplied
Auckland Rescue Helicopter chief crewman Mark Cannell carrying the injured child. Photo / Supplied

The mother and daughter were flown to North Shore Hospital and a Waitemata District Health Board spokesman said the woman was stable, and the child had been discharged.

Auckland Rescue Helicopter chief crewman Mark Cannell said the collision between the two cars looked "hefty".

"The impact looked very frontal so airbags had been deployed."

The pair had been wearing seatbelts at the time of the impact and the mother was conscious but in a lot of pain, he said.

There had been light showers and the road wasn't well lit. Everyone had been removed from the cars by the time the helicopters arrived.

The road was temporarily blocked off while the Serious Crash Unit investigated and a police spokeswoman said inquiries were continuing.

The official Christmas New Year holiday period began at 4pm yesterday and ends at 6am on January 3.

In that period between 2016 and 2017 there were 15 fatal crashes and 313 injuries.

The toll was off to a sad start on Saturday morning after another crash in central Auckland which killed one.